i pull a 5k lb camper, and had to get a new hitch when i bought the hummer, to maintain some kind of level tow. camping world has a good variety of the heavy duty hitches to lower the ball mount to keep the trailer level, and your boat dealer probably does too. i don't know enough about towing to know if the angle caused your problem or not. i've also got the load leveling bars for the trailer that helps stabilize the back end of the bus. do you have air rear suspension or springs? i went from towing with a supercahrged 4runner to the H2, so i don't have an apple-to-apple comparison like you do with your denali. the H2 does a far better job, but hills are still a bit disappointing.